Taliban fighters have seized most of Kunduz Province’s capital in northern Afghanistan after hours of clashes with security forces.

Provincial police spokesman Sayed Sarwar Hussaini said the militants captured more than half of the city on September 28, hours after launching an assault from several directions around dawn.

Hussaini said militants captured a number of government buildings, including Kunduz's main prison, and freed about 500 prisoners.

A spokesman said Afghan President Ashraf Ghani was in "constant contact" with security commanders in Kunduz, where the situation was "fluid."

Dozens of Afghan special forces have been flown into Kunduz airport on a C-130 aircraft and were preparing to launch a counter-attack to retake the city, an Afghan official told the Reuters news agency.

The Taliban said it had seized the provincial government headquarters in Kunduz and were moving towards the main airport where some government officials had fled.

"With capturing of police compound and governor's office in Kunduz, the whole province fell to our hands and our fighters are now advancing towards the airport," the Islamist militant movement's spokesman, Zabihullah Mujahid, said on his Twitter account.

A senior government official confirmed to Reuters that the provincial headquarters had fallen to the insurgents.

The Reuters news agency reported that Taliban fighters had hoisted their flag over the main intersection of the city of around 300,000 people.

“Heavy fighting continues in the city center,” provincial deputy governor Hamdulla Daneshi told RFE/RL’s Radio Free Afghanistan. “The city is divided in two parts and it’s turned completely to a warzone.”

"Security forces in Kunduz were prepared for an attack but not one of this size, and not one that was coordinated in 10 different locations at the same time," Interior Ministry spokesman Sediq Sediqqi said.

Government officials said reinforcements were being sent to the city.

Police said there were casualties on both sides.

The United Nations Assistance Mission in Afghanistan evacuated its Kunduz compound on September 28, soon after the assault began.

"They've been relocated within Afghanistan," said UN spokesman Dominic Medley, declining to say where or how many staff were evacuated.

The once-quiet north of Afghanistan has seen escalating violence in recent years.

Kunduz city was the center of fierce fighting in April as the Taliban sought to gain territory after NATO ended its combat mission in Afghanistan last December and pulled out the bulk of its troops.

Kunduz Province contains major roads that connect central and northern Afghanistan, including a road to the capital, Kabul.

The attack comes a day after a suicide attack at a game of cricket in the eastern province of Paktika killed at least nine people and wounded more than 30.

There was no immediate claim of responsibility.

The explosion was caused by a motorcycle bomb, local officials said, and probably targeted local government officials watching the match.

A similar attack last year at a volleyball match killed at least 50 people in the same province.

Earlier on September 27, Afghan officials said Islamic State (IS) militants attacked checkpoints in Nangarhar Province, killing three police officers.

Provincial government spokesman Ahmad Zia Abdulzai said another eight policemen were wounded in the attack in the Achin district, bordering Pakistan.

He also said Afghan air strikes launched after the early morning attack killed 60 IS militants.

A UN report published on September 25 warned that IS was making inroads in Afghanistan, winning over a growing number of sympathizers and recruiting followers in 25 of the country's 34 provinces.